Switched mode power supplies as main parts of telecom and commercial systems often dictate their size and electrical performance as well as reliability and costs. As requirements for the key characteristics power density and efficiency of power converters increase, the demands of these evaluation characteristics increase for inductive components particularly. One approach of increasing the power density and the efficiency is to integrate inductive components. Transformers and inductors can be integrated into a single magnetic structure which than reduces cost, increases power density and power efficiency.
A power converter where integrated magnetics are strongly recommended is the LLC resonant converter, which is capable of yielding high efficiency and high-quality EMI while operating at high switching frequency. U.S. Pat. No. 6,344,979 B1 discloses an insulating type DC-DC converter capable of insulating a voltage of a direct current power source and outputting a direct current to a load as shown in FIG. 1. It comprises LLC converter according to the prior art which uses three magnetic components: a series resonant inductor, a parallel resonant inductor, a two-winding or three-winding transformer. This converter results, additionally to the number of discrete magnetic components which yield higher size and costs, in at least three windings and several interconnections which negatively impact the efficiency.
A further type of power converter where integrated magnetic circuits are strongly recommended is the soft-switching converter.
In recent years some efforts were done to integrate all three magnetic components into a single component for LLC resonant converter. US 2008 0224 809 discloses an integrated magnetic structure (FIG. 2) that helps to increase power density as well as efficiency. Core losses are reduced by means of flux compensation in mutual core flanges and copper losses are minimized by reduction of interconnections between resonance choke and transformer. Mutual core flanges imply increase of power density.
Despite all the benefits of the LLC converter in terms of efficiency and EMI there are still some drawbacks. In a lot of application there is a need for over-current protection. US 2011 0255 321 discloses a LLC resonant converter capable of overcurrent protection. However, this circuit implies even more discrete magnetic components and more interconnections which increase the volume drastically and damage the efficiency gains. Also the above mentioned structure disclosed in US 2008 0224 809 is not suitable for such complex converters with more than one filter chokes and especially not for converter with split resonant chokes. Distributing the inductive components over more than one magnetic component would not only minimize losses and increase the volume, but may also deteriorate the EMI quality.